I Need Your Suggestions!

Okay,
Im just starting on this forum thing cause I wanted to see what other people thought of my horses problem ....

I have had her for 14 years and have used the same saddle over those years, she has never had a problem with it until now! About 2 weeks ago, she seemed to spook when I tightened the girth, just when tacking up not once it was on, and have continued since. I rode her today and she rather trot then canter (i figured she was just being lazy, a common thing from her) but then she started hitting the rails one by one (most deffinately not a common thing). I know these are things meaning the saddle doesnt fit ... but can a saddle go from fitting to not? Especially with all this time of using it?

Please I need answers ! Anyone can help :)

I would just question whether she has gained or lost weight to make a difference in the saddle fit.